Conventional rotation detecting apparatuses detect a rotational angle of a motor and the number of rotations of the motor. For example, Japanese Patent Publication No. 5958572, which will be referred to as a published patent document, discloses an example of these conventional rotation detecting apparatuses.
Specifically, the conventional rotation detecting apparatus disclosed in the published patent document, which is installed in a vehicle, is activated upon a power supply switch, i.e. an ignition switch, of the vehicle being in an on state so that electrical power is supplied from a power source to the conventional rotation detecting apparatus via the ignition switch.
The conventional rotation detecting apparatus includes a rotation sensor that obtains a measurement signal related to rotations of the motor. The conventional rotation detecting apparatus calculates, based on the measurement signal obtained by the rotation sensor, first rotation-related information indicative of a rotational angle of the motor upon the ignition switch of the vehicle being in the on state.
The conventional rotation detecting apparatus therefore stops calculation of the first rotation-related information upon the ignition switch being in an off state, because no electrical power is supplied from the power source to the conventional rotation detecting apparatus.
The conventional rotation detecting apparatus disclosed in the published patent document also calculates, based on the measurement signal obtained by the rotation sensor, second rotation-related information indicative of the number of rotations of the motor using electrical power supplied from the power source independently of the on/off state of the ignition switch.
This configuration of the conventional rotation detecting apparatus aims to reduce power consumption of the conventional rotation detecting apparatus upon the ignition switch being in the off state.